include ../_util-fns

:marked
  We’ve all used a form to login, submit a help request, place an order, book a flight,
  schedule a meeting and perform countless other data entry tasks.
  Forms are the mainstay of business applications.

  Any seasoned web developer can slap together an HTML form with all the right tags.
  It's more challenging to create a cohesive data entry experience that guides the
  user efficiently and effectively through the workflow behind the form.

  *That* takes design skills that are, to be frank, well out of scope for this chapter.

  It also takes framework support for
  **two-way data binding, change tracking, validation, and error handling**
  ... which we shall cover in this chapter on Angular forms.

  We will build a simple form from scratch, one step at a time. Along the way we'll learn

  * How to build an Angular form with a component and template

  * The `ngModel` two-way data binding syntax for reading and writing values to input controls

  * The `ngModel` directive in combination with a form to track the change state and validity of form controls

  * The Special CSS classes that follow the state of the controls and can be used to provide strong visual feedback

  * How to display validation errors to users and enable/disable form controls

  * How to share information across controls with template local variables
  
  <live-example>Live Example</live-example>

.l-main-section
:marked
   ## Bootstrap

   We start by showing how to bootstrap the application and add the necessary dependencies to use forms.

   During bootstrap we have to register the new forms module by calling `provideForms()` and pass the result to the provider array. 
+makeExample('forms/js/src/main.js','','src/main.js')   

:marked
   The old forms API is going through a deprecation phase. During this transition Angular is supporting both form modules. 

   To remind us that the old API is deprecated, Angular will print a warning message to the console. 
   
   Since we are converting to the new API, and no longer need the old API, we call `disableDeprecatedForms()` to disable the old form functionality and the warning message. 

.l-main-section
:marked
  ## Template-Driven Forms

  Many of us will build forms by writing templates in the Angular [template syntax](./template-syntax.html) with
  the form-specific directives and techniques described in this chapter.
.l-sub-section
  :marked
    That's not the only way to create a form but it's the way we'll cover in this chapter.
:marked
  We can build almost any form we need with an Angular template &mdash; login forms, contact forms ... pretty much any business forms.
  We can lay out the controls creatively, bind them to data, specify validation rules and display validation errors,
  conditionally enable or disable specific controls, trigger built-in visual feedback, and much more.

  It will be pretty easy because Angular handles many of the repetitive, boiler plate tasks we'd
  otherwise wrestle with ourselves.

  We'll discuss and learn to build the following template-driven form:

figure.image-display
  img(src="/resources/images/devguide/forms/hero-form-1.png" width="400px" alt="Clean Form")

:marked
  Here at the *Hero Employment Agency* we use this form to maintain personal information about the
  heroes in our stable. Every hero needs a job. It's our company mission to match the right hero with the right crisis!

  Two of the three fields on this form are required. Required fields have a green bar on the left to make them easy to spot.

  If we delete the hero name, the form displays a validation error in an attention grabbing style:

figure.image-display
  img(src="/resources/images/devguide/forms/hero-form-2.png" width="400px" alt="Invalid, Name Required")

:marked
  Note that the submit button is disabled and the "required" bar to the left of the input control changed from green to red.

.l-sub-section
  p We'll' customize the colors and location of the "required" bar with standard CSS.

:marked
  We will build this form in the following sequence of small steps

  1. Create the `Hero` model class
  1. Create the component that controls the form
  1. Create a template with the initial form layout
  1. Add the **ngModel** directive to each form input control
  1. Add the **#name** attribute to each form input control
  1. Add custom CSS to provide visual feedback
  1. Show and hide validation error messages
  1. Handle form submission with **ngSubmit**
  1. Disable the form’s submit button until the form is valid

:marked
  ## Setup
  Create a new project folder (`angular-forms`) and follow the steps in the [QuickStart](../quickstart.html).

  ## Create the Hero Model Class

  As users enter form data, we capture their changes and update an instance of a model.
  We can't layout the form until we know what the model looks like.

  A model can be as simple as a "property bag" that holds facts about a thing of application importance.
  That describes well our `Hero` class with its three required fields (`id`, `name`, `power`)
  and one optional field (`alterEgo`).

  Create a new file in the app folder called `hero.js` and give it the following constructor:

+makeExample('forms/js/src/app/hero.js', null, 'src/app/hero.js')

:marked
  It's an anemic model with few requirements and no behavior. Perfect for our demo.
  
  The `alterEgo` is optional and the constructor lets us omit it by being the last argument.

  We can create a new hero like this:
code-example(format="").
  var myHero =  new Hero(42, 'SkyDog', 
                         'Fetch any object at any distance', 'Leslie Rollover');
  console.log('My hero is called ' + myHero.name); // "My hero is called SkyDog"
:marked
  We update the `<head>` of the `index.html` to include this javascript file.

+makeExample('forms/js/src/index.html', 'scripts-hero', 'src/index.html (excerpt)')(format=".")

.l-main-section
:marked
  ## Create a Form component

  An Angular form has two parts: an HTML-based template and a code-based Component to handle data and user interactions.

  We begin with the Component because it states, in brief, what the Hero editor can do.

  Create a new file called `hero-form.component.js` and give it the following definition:

+makeExample('forms/js/src/app/hero-form.component.js', 'first', 'src/app/hero-form.component.js')

:marked
  There’s nothing special about this component, nothing form-specific, nothing to distinguish it from any component we've written before.

  Understanding this component requires only the Angular concepts we’ve learned in previous chapters

  * We use the `ng.core` object from the Angular library as we usually do.

  * The `Component()` selector value of "hero-form" means we can drop this form in a parent template with a `<hero-form>` tag.

  * The `templateUrl` property points to a separate file for template HTML called `hero-form.component.html`.

  * We defined dummy data for `model` and `powers` as befits a demo.
  
  Down the road, we can inject a data service to get and save real data
  or perhaps expose these properties as [inputs and outputs](./template-syntax.html#inputs-outputs) for binding to a
  parent component. None of this concerns us now and these future changes won't affect our form.

  * We threw in a `diagnostic` method at the end to return a JSON representation of our model.
  It'll help us see what we're doing during our development; we've left ourselves a cleanup note to discard it later.

  Why don't we write the template inline in the component file as we often do
  elsewhere in the Developer Guide?

  There is no “right” answer for all occasions. We like inline templates when they are short.
  Most form templates won't be short. TypeScript and JavaScript files generally aren't the best place to
  write (or read) large stretches of HTML and few editors are much help with files that have a mix of HTML and code.
  We also like short files with a clear and obvious purpose like this one.

  We made a good choice to put the HTML template elsewhere. 
  We'll write that template in a moment. Before we do, we'll take a step back
  and revise the `app.component.js` to make use of our new `HeroFormComponent`.
  
:marked
  Again we update the `<head>` of the `index.html` to include the new javascript file.

+makeExample('forms/js/src/index.html', 'scripts-hero-form', 'src/index.html (excerpt)')(format=".")  

.l-main-section
:marked
  ## Revise the *app.component.js*

  `app.component.js` is the application's root component. It will host our new `HeroFormComponent`.

  Replace the contents of the "QuickStart" version with the following:
+makeExample('forms/js/src/app/app.component.js', null, 'src/app/app.component.js')

:marked
.l-sub-section
  :marked
    There are only two changes:

    1. The `template` is simply the new element tag identified by the component's `select` property.

    1. The `directives` array tells Angular that our template depends upon the `HeroFormComponent`
    which is itself a Directive (as are all Components).

.l-main-section
:marked
  ## Create an initial HTML Form Template

  Create a new template file called `hero-form.component.html` and give it the following definition:

+makeExample('forms/js/src/app/hero-form.component.html', 'start', 'src/app/hero-form.component.html')

:marked
  That is plain old HTML 5. We're presenting two of the `Hero` fields, `name` and `alterEgo`, and
  opening them up for user input in input boxes.

  The *Name* `<input>` control has the HTML5 `required` attribute;
  the *Alter Ego* `<input>` control does not because `alterEgo` is optional.

  We've got a *Submit* button at the bottom with some classes on it.

  **We are not using Angular yet**. There are no bindings. No extra directives. Just layout.

  The `container`,`form-group`, `form-control`, and `btn` classes 
  come from [Twitter Bootstrap](http://getbootstrap.com/css/). Purely cosmetic.
  We're using Bootstrap to gussy up our form.
  Hey, what's a form without a little style!

.callout.is-important
  header Angular Forms Do Not Require A Style Library
  :marked
    Angular makes no use of the `container`, `form-group`, `form-control`, and `btn` classes or
    the styles of any external library. Angular apps can use any CSS library
    ... or none at all.

:marked
  Let's add the stylesheet. Open <code>index.html</code> and add the following link to the <code>&lt;head></code>.
+makeExample('forms/js/src/index.html', 'bootstrap')(format=".")

:marked
.l-main-section
:marked
  ## Add Powers with ***ngFor**
  Our hero may choose one super power from a fixed list of Agency-approved powers.
  We maintain that list internally (in `HeroFormComponent`).

  We'll add a `select` to our
  form and bind the options to the `powers` list using `NgFor`,
  a technique we might have seen before in the [Displaying Data](./displaying-data.html) chapter.

  Add the following HTML *immediately below* the *Alter Ego* group.
+makeExample('forms/js/src/app/hero-form.component.html', 'powers', 'src/app/hero-form.component.html (excerpt)')(format=".")

:marked
  We are repeating the `<options>` tag for each power in the list of Powers.
  The `#p` local template variable is a different power in each iteration;
  we display its name using the interpolation syntax with the double-curly-braces.

.l-main-section
:marked
  ## Two-way data binding with ***ngModel**
  Running the app right now would be disappointing.

figure.image-display
  img(src="/resources/images/devguide/forms/hero-form-3.png" width="400px" alt="Early form with no binding")
:marked
  We don't see hero data because we are not binding to the `Hero` yet.
  We know how to do that from earlier chapters.
  [Displaying Data](./displaying-data.html) taught us Property Binding.
  [User Input](./user-input.html) showed us how to listen for DOM events with an
  Event Binding and how to update a component property with the displayed value.

  Now we need to display, listen, and extract at the same time.

  We could use those techniques again in our form.
  Instead we'll introduce something new, the `NgModel` directive, that
  makes binding our form to the model super-easy.

  Find the `<input>` tag for the "Name" and update it like this

+makeExample('forms/js/src/app/hero-form.component.html', 'ngModel-1','src/app/hero-form.component.html (excerpt)')(format=".")

.l-sub-section
  :marked
    We appended a diagnostic interpolation after the input tag
    so we can see what we're doing.
    We left ourselves a note to throw it way when we're done.

:marked
  Focus on the binding syntax: `[(ngModel)]="..."`.

  If we ran the app right now and started typing in the *Name* input box,
  adding and deleting characters, we'd see them appearing and disappearing
  from the interpolated text.
  At some point it might look like this.
figure.image-display
  img(src="/resources/images/devguide/forms/ng-model-in-action.png" width="400px" alt="ngModel in action")
:marked
  The diagnostic is evidence that we really are flowing values from the input box to the model and
  back again. **That's two-way data binding!**

  Notice that we also added a `name` attribute to our `<input>` tag. This is a requirement when using `[(ngModel)]` in combination with a form, so that we can easily refer to it in the aggregate form value and validity state.

  Let's add similar `[(ngModel)]` bindings to *Alter Ego* and *Hero Power*.
  We'll ditch the input box binding message
  and add a new binding at the top to the component's `diagnostic` method.
  Then we can confirm that two-way data binding works *for the entire Hero model*.

  After revision the core of our form should have three `[(ngModel)]` bindings that
  look much like this:

+makeExample('forms/js/src/app/hero-form.component.html', 'ngModel-2', 'src/app/hero-form.component.html (excerpt)')

:marked
  If we ran the app right now and changed every Hero model property, the form might display like this:
figure.image-display
  img(src="/resources/images/devguide/forms/ng-model-in-action-2.png" width="400px" alt="ngModel in super action")
:marked
  The diagnostic near the top of the form
  confirms that all of our changes are reflected in the model.

  **Delete** the `{{diagnostic()}}` binding at the top as it has served its purpose.

.l-sub-section
  :marked
    ### Inside [(ngModel)]
    *This section is an optional deep dive into [(ngModel)]. Not interested? Skip ahead!*
    
    The punctuation in the binding syntax, <span style="font-family:courier"><b>[()]</b></span>, is a good clue to what's going on.

    In a Property Binding, a value flows from the model to a target property on screen.
    We identify that target property by surrounding its name in brackets, <span style="font-family:courier"><b>[]</b></span>.
    This is a one-way data binding **from the model to the view**.

    In an Event Binding, we flow the value from the target property on screen to the model.
    We identify that target property by surrounding its name in parentheses, <span style="font-family:courier"><b>()</b></span>.
    This is a one-way data binding in the opposite direction **from the view to the model**.

    No wonder Angular chose to combine the punctuation as <span style="font-family:courier"><b>[()]</b></span>
    to signify a two-way data binding and a **flow of data in both directions**.

    In fact, we can break the `NgModel` binding into its two separate modes
    as we do in this re-write of the "Name" `<input>` binding:
  +makeExample('forms/js/src/app/hero-form.component.html', 'ngModel-3','src/app/hero-form.component.html (excerpt)')(format=".")

  :marked
    <br>The Property Binding should feel familiar. The Event Binding might seem strange.

    The `ngModelChange` is not an `<input>` element event.
    It is actually an event property of the `NgModel` directive.
    When Angular sees a binding target in the form <span style="font-family:courier">[(x)]</span>,
    it expects the `x` directive to have an `x` input property and an `xChange` output property.

    The other oddity is the template expression, `model.name = $event`.
    We're used to seeing an `$event` object coming from a DOM event.
    The `ngModelChange` property doesn't produce a DOM event; it's an Angular `EventEmitter`
    property that returns the input box value when it fires &mdash; which is precisely what
    we should assign to the model's `name' property.

    Nice to know but is it practical? We almost always prefer `[(ngModel)]`.
    We might split the binding if we had to do something special in
    the event handling such as debounce or throttle the key strokes.

    Learn more about `NgModel` and other template syntax in the
    [Template Syntax](./template-syntax.html) chapter.

.l-main-section
:marked
  ## Track change-state and validity with **ngModel**

  A form isn't just about data binding. We'd also like to know the state of the controls on our form.

  Using `ngModel` in a form gives us more than just two way data binding. It also tells us if the user touched the control, if the value changed, or if the value became invalid.

  `ngModel` doesn't just track state; it updates the control with special Angular CSS classes from the set we listed above.
  We can leverage those class names to change the appearance of the
  control and make messages appear or disappear.

  We'll explore those effects soon. Right now
  let's make sure we have `ngModel` and the corresponding name attribute on all three form controls,
  starting with the *Name* input box.
+makeExample('forms/js/src/app/hero-form.component.html', 'ngModelName-1', 'src/app/hero-form.component.html (excerpt)')(format=".")
:marked
  We set the `name` attribute to "name" which makes sense for our app. Any unique value will do.

.l-sub-section
  :marked
    Internally Angular creates `FormControls` and registers them with an `NgForm` directive that Angular attached to the `<form>` tag. Each `FormControl` is registered under the name we assigned to the `name` attribute.
    We'll talk about `NgForm` [later in the chapter](#ngForm).

.l-main-section
:marked
  ## Add Custom CSS for Visual Feedback

  `NgModel` doesn't just track state. 
  It updates the control with three classes that reflect the state.
  
table
  tr
    th State
    th Class if true
    th Class if false
  tr
    td Control has been visited
    td <code>ng-touched</code>
    td <code>ng-untouched</code>
  tr
    td Control's value has changed
    td <code>ng-dirty</code>
    td <code>ng-pristine</code>
  tr
    td Control's value is valid
    td <code>ng-valid</code>
    td <code>ng-invalid</code>
:marked
  Let's add a temporary [local template variable](./template-syntax.html#local-vars) named **spy**
  to the "Name" `<input>` tag and use the spy to display those classes.

+makeExample('forms/js/src/app/hero-form.component.html', 'ngModelName-2','src/app/hero-form.component.html (excerpt)')(format=".")

:marked
  Now run the app and focus on the *Name* input box.
  Follow the next four steps *precisely*

  1. Look but don't touched
  1. Click in the input box, then click outside the text input box
  1. Add slashes to the end of the name
  1. Erase the name

  The actions and effects are as follows:
figure.image-display
  img(src="/resources/images/devguide/forms/control-state-transitions-anim.gif"  alt="Control State Transition")
:marked
  We should be able to see the following four sets of class names and their transitions:
figure.image-display
  img(src="/resources/images/devguide/forms/ng-control-class-changes.png" width="400px" alt="Control State Transitions")

:marked
  The (`ng-valid` | `ng-invalid`) pair are most interesting to us. We want to send a
  strong visual signal when the data are invalid and we want to mark required fields.

  We realize we can do both at the same time with a colored bar on the left of the input box:

figure.image-display
  img(src="/resources/images/devguide/forms/validity-required-indicator.png" width="400px" alt="Invalid Form")

:marked
  We achieve this effect by adding two styles to a new `forms.css` file
  that we add to our project as a sibling to `index.html`.

+makeExample('forms/js/src/forms.css',null,'src/forms.css')(format=".")
:marked
  These styles select for the two Angular validity classes and the HTML 5 "required" attribute.

  We update the `<head>` of the `index.html` to include this style sheet.
+makeExample('forms/js/src/index.html', 'styles', 'src/index.html (excerpt)')(format=".")
:marked
  ## Show and Hide Validation Error messages

  We can do better.

  The "Name" input box is required. Clearing it turns the bar red. That says *something* is wrong but we
  don't know *what* is wrong or what to do about it.
  We can leverage the `ng-invalid` class to reveal a helpful message.

  Here's the way it should look when the user deletes the name:
figure.image-display
  img(src="/resources/images/devguide/forms/name-required-error.png" width="400px" alt="Name required")

:marked
  To achieve this effect we extend the `<input>` tag with
  1. a [local template variable](./template-syntax.html#local-vars)
  1. the "*is required*" message in a nearby `<div>` which we'll display only if the control is invalid.

  Here's how we do it for the *name* input box:
-var stylePattern = { otl: /(#name=&quot;form&quot;)|(.*div.*$)|(Name is required)/gm };
+makeExample('forms/js/src/app/hero-form.component.html', 
  'name-with-error-msg', 
  'src/app/hero-form.component.html (excerpt)', 
  stylePattern)
:marked
  We need a template reference variable to access the input box's Angular control from within the template.
  Here we created a variable called `name` and gave it the value "ngModel".
.l-sub-section
  :marked
    Why "ngModel"? 
    A directive's [exportAs](../api/core/index/Directive-decorator.html) property 
    tells Angular how to link the reference variable to the directive.
    We set `name` to `ngModel` because the `ngModel` directive's `exportAs` property happens to be "ngModel".
    
    Now we can control visibility of the "name" error message by binding properties of the `name` control to the message `<div>` element's `hidden` property.
    
    The message is hidden while the control is valid; the message is revealed when the control becomes invalid.
<a id="ngForm"></a>
.l-sub-section
  :marked
    ### The NgForm directive
    We just set a template local variable with the value of an `NgForm` directive. 
    Why did that work? We didn't add the **[`NgForm`](../api/forms/index/NgForm-directive.html) directive** explicitly.
    
    Angular added it surreptitiously, wrapping it around the `<form>` element

    The `NgForm` directive  supplements the `form` element with additional features.
    It holds the controls we created for the elements with `ngModel` directive and `name` attribute
    and monitors their properties including their validity.
    It also has its own `valid` property which is true only if every contained
    control is valid.
:marked
  The Hero *Alter Ego* is optional so we can leave that be.

  Hero *Power* selection is required.
  We can add the same kind of error handling to the `<select>` if we  want
  but it's not imperative because the selection box already constrains the
  power to valid value.

.l-main-section
:marked
  ## Submit the form with **ngSubmit**
  The user should be able to submit this form after filling it in.
  The Submit button at the bottom of the form
  does nothing on its own but it will
  trigger a form submit because of its type (`type="submit"`).

  A "form submit" is useless at the moment.
  To make it useful, we'll update the `<form>` tag with another Angular directive, `NgSubmit`,
  and bind it to the `HeroFormComponent.submit()` method with an  event binding
+makeExample('forms/js/src/app/hero-form.component.html', 'ngSubmit')(format=".")

:marked
  We slipped in something extra there at the end!  We defined a
  template local variable, **`#heroForm`**, and initialized it with the value, "ngForm".

  The variable `heroForm` is now a handle to the `NgForm` directive that we [discussed earlier](#ngForm)
  This time `heroForm` remains a reference to the form as a whole.

  Later in the template we bind the button's `disabled` property to the form's over-all validity via
  the `heroForm` variable. Here's that bit of markup:
+makeExample('forms/js/src/app/hero-form.component.html', 'submit-button')
:marked
  Re-run the application. The form opens in a valid state and the button is enabled.

  Now delete the *Name*. We violate the "name required" rule which
  is duly noted in our error message as before. And now the Submit button is also disabled.

  Not impressed?  Think about it for a moment. What would we have to do to
  wire the button's enable/disabled state to the form's validity without Angular's help?

  For us, it was as simple as
  1. Define a template local variable on the (enhanced) form element
  2. Reference that variable in a button some 50 lines away.

.l-main-section
:marked
  ## Toggle two form regions (extra credit)
  Submitting the form isn't terribly dramatic at the moment.
.l-sub-section
  :marked
    An unsurprising observation for a demo. To be honest,
    jazzing it up won't teach us anything new about forms.
    But this is an opportunity to exercise some of our newly won
    binding skills.
    If you're not interested, you can skip to the chapter's conclusion
    and not miss a thing.
:marked
  Let's do something more strikingly visual.
  Let's hide the data entry area and display something else.

  Start by wrapping the form in a `<div>` and bind
  its `hidden` property to the `HeroFormComponent.submitted` property.

+makeExample('forms/js/src/app/hero-form.component.html', 'edit-div', 'src/app/hero-form.component.html (excerpt)')(format=".")

:marked
  The main form is visible from the start because the
  the `submitted` property is false until we submit the form,
  as this fragment from the `HeroFormComponent` reminds us:

+makeExample('forms/js/src/app/hero-form.component.js', 'submitted')(format=".")

:marked
  When we click the Submit button, the `submitted` flag becomes true and the form disappears
  as planned.

  Now we need to show something else while the form is in the submitted state.
  Add the following block of HTML below the `<div>` wrapper we just wrote:
+makeExample('forms/js/src/app/hero-form.component.html', 'submitted', 'src/app/hero-form.component.html (excerpt)')

:marked
  There's our hero again, displayed read-only with interpolation bindings.
  This slug of HTML only appears while the component is in the submitted state.

  We added an Edit button whose click event is bound to an expression
  that clears the `submitted` flag.

  When we click it, this block disappears and the editable form reappears.

  That's as much drama as we can muster for now.

.l-main-section
:marked
  ## Conclusion

  The Angular form discussed in this chapter takes advantage of the following framework features to provide support for data modification, validation and more:

  - An Angular HTML form template.
  - A form component class with a `Component` decorator.
  - The `ngSubmit` directive for handling the form submission.
  - Template local variables such as `#heroForm`, `#name`, `#alter-ego` and `#power`.
  - The `[(ngModel)]` syntax for two-way data binding, validation and change tracking.
  - The local variable’s `valid` property on input controls to check if a control is valid and show/hide error messages.
  - Controlling the submit button's enabled state by binding to `NgForm` validity.
  - Custom CSS classes that provide visual feedback to users about invalid controls.

  Our final project folder structure should look like this:
.filetree
  .file angular-forms
  .children
    .file node_modules ...
    .file src
    .children
      .file app
      .children
        .file app.component.js
        .file hero.js
        .file hero-form.component.html
        .file hero-form.component.js
      .file main.ts
      .file forms.css
      .file index.html
      .file tsconfig.json
    .file package.json
:marked
  Here’s the final version of the source:

+makeTabs(
  `forms/js/src/app/hero-form.component.js,
   forms/js/src/app/hero-form.component.html,
   forms/js/src/app/hero.js,
   forms/js/src/app/app.module.js,
   forms/js/src/app/app.component.js,
   forms/js/src/main.js,   
   forms/js/src/index.html,
   forms/js/src/forms.css`,
  'final, final,,,,,',
  `app/hero-form.component.js,
   app/hero-form.component.html,   
   app/hero.js,
   app/app.module.js,
   app/app.component.js,
   main.js,
   index.html,
   forms.css`)
:marked
